1. Technical Field
The present invention relates generally to an apparatus for mounting a feedthrough member into a housing and, more particularly, to an apparatus for mounting either a window or a conduction member into a housing which reduces the internal stress in the apparatus resulting from ambient temperature variations.
2. Discussion
Waveguide windows and feedthrough assemblies allow electromagnetic energy to interact between components located in an enclosed circuit network and those located in an external environment. These apparatuses generally include a feedthrough member which transmits or conducts externally propagating energy into the circuit network, a frame member which reinforces the feedthrough member and allows it to be appropriately positioned relative to the circuit network and a housing which encloses the circuit network.
A waveguide window directs electromagnetic energy propagating in the atmosphere into the circuit network through a window that is transparent to the electromagnetic energy. The waveguide window material typically incorporates a low dielectric constant and low loss factor material, such as fused silica. A feedthrough assembly allows an external transmission line in which electromagnetic energy is propagated to be connected to a conduction member to conduct the energy directly into the circuit network. The conduction member generally is constructed of a metal conductor core surrounded by an insulating sleeve.
In addition to their desirable properties, the material of these feedthrough members typically has a low coefficient of thermal expansion (CTE) and low strength. In an effort to prevent failure of the waveguide window or conduction member, a frame member made of material with a low coefficient of thermal expansion but a substantially higher strength is used to mount the feedthrough member into the housing of the circuit network. In an effort to minimize the weight of the housing a lightweight material, such as aluminum, is preferred. These materials typically have a relatively high coefficient of thermal expansion (CTE).
High internal stress levels can be generated during temperature changes as a result of the vast differences in the CTEs of the circuit network components. These high stress levels can deteriorate or destroy the feedthrough member or cause separation of the interface between the feedthrough member and the housing.
The prior art shows structural modifications to the frame member such as grooves, to provide stress relief. These have been of limited effectiveness particularly at the interface of the dissimilar materials. Accordingly, there is a need to provide an improved waveguide window or feedthrough apparatus for reducing the internal stress level and increasing the longevity, reliability and durability of the apparatus.